Reserving the covenant of redemption for a separate treatment is warranted because many Christian Theologians, as noted in part above, restrict the covenant concept to only those “transactions” that occur in Biblical history and therefore don't consider what is typically referred to by this covenant as a covenant in any sense at all. Consequently, it is dropped from the discussion. However, though not explicitly named a covenant of redemption, the WCF points to the intratrinitarian commitment that lays the groundwork for the works principle manifested in the covenant of works and the plan of redemption (which itself is based on Christ fulfilling his covenant of works made with the Father):
It pleased God , in his eternal purpose, to choose and ordain the Lord Jesus, his only begotten son, to be the mediator between God and man, the Prophet, Priest and King, the Head and Savior of his church, the Heir of all things, and Judge of the world: unto whom from all eternity give a people, to be his seed, and to be by him in time redeemed, called, justified, sanctified, and glorified1.
And further in the confession:
The Lord Jesus, in His human nature thus united to the divine, was sanctified, and anointed with the Holy Spirit, above measure, having in Him all the treasures of wisdom and knowledge; in whom it pleased the Father that all fullness should dwell; to the end that, being holy, harmless, undefiled, and full of grace and truth, He might be thoroughly furnished to execute the office of a Mediator and Surety. Which office He took not unto Himself, but was thereunto called by His Father, who put all power and judgment into His hand, and gave Him commandment to execute the same.2
The covenant of redemption is different from all other covenants on three counts. The first is that it is the only covenant that is made not between God and man, but between the persons of the trinity. The second is that it is the only covenant not named as such even if implicitly.3 Thirdly, the covenant of redemption, precisely because it was not initiated at some specific place and time in the history of creation is not a covenant whose defenders can point to a specific passage that details it fully.
Essentially, the covenant of redemption is a works covenant. The pledge “this I will do” forms the basis of the covenant. God the Father elects a rebellious covenant breaking people for himself which he promises to give as an inheritance to his Son. God the Son promises to work as the second Adam (and as the true Israel) in order to reconcile the rebellious elect to the Father. God the Spirit promises to effectually bring these rebellious elect to saving belief in the Son.
1WCF Ch. 8, P1.
2WCF Ch. 8, P3.
3The Davidic covenant of 2 Sam. 7 is not named a covenant during the historical event when it is announced but is referred to as a covenant in Psalm 89:3. Likewise, the Adamic covenant of works is referred to as a covenant in Hosea 6:7.